Center fed wire antenna with sheet reflector and impedance matching coupling to coaxial transmission line



March 25, 1968 R. E. FISK ETAL 3,375,525

CENTER FED WIRE ANTENNA WITH SHEET REFLECTOR AND IMPEDANCE MATCHING COUPLING TO COAXIAL TRANSMISSION LINE Filed June 16, 1965 FIG.3.

7'? W W W F INVENTORS:

JOSE PERINI, RONALD E. FISK,

United States Patent York Filed June 16, 1965, Ser. No. 464,442 9 Claims. (Cl. 343-863) The present invention relates to coupling means for an antenna system, and more particularly relates to means for coupling power from a transmission line of one characteristic impedance to an antenna having an input impedance diiferent in character and higher in value than the characteristic impedance of the transmission line.

The invention has particular application to a zig-zag panel type of antenna comprising a pair of zig-zag radiative conductors extending in opposite directions from a common point of energization and a planar reflector spaced in radiative relationship therewith. Such antennas have an input impedance which is high in relation to the characteristic impedance of normally available transmission lines and which is usually complex in nature, i.e., has a reactive component. In order to minimize undesired reflections in the complete system which cause a dissipation of power, and are apt to cause arcing in the system, provision must be made for matching the impedance of the antenna to the characteristic impedance of the transmission line.

An object of the present invention is to provide a simple coupling means which matches the complex impedance of high value of the antenna to the characteristic impedance of low value of the transmission line supplying energization thereto.

It is another object of the present invention to provide a means which can be readily adjusted to provide optimum match of the impedance of the antenna to the impedance of the transmission line supplying the antenna with energization.

In accordance with an illustrative embodiment of the invention there is provided a strap conductor of appropriate configuration connected at one end to the radiative conductors and at the other end thereof to the inner conductor of a coaxial transmission line. The transmission line formed by the strap conductor and reflector is tapered in impedance from a high value in the vicinity of the input to the radiative conductors of the antenna to a low value in the vicinity of the coaxial transmission line. The strap conductor is of the order of one-quarter wavelength long at the frequency of operation of the system and is shaped to provide a lumped reactance at the coaxial transmission line end thereof to tune out the capacitive react ance of antenna input impedance.

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIGURE 1 is a front view of a zig-zag panel antenna system in accordance with the present invention;

FIGURE 2 is a side view of the antenna system of FIGURE 1;

FIGURE 3 is an enlarged front view of the center section of the antenna system showing the coupling means thereof in accordance with the present invention;

FIGURE 4 is an enlarged side view of the coupling system of FIGURE 3.

Referring now to FIGURES 1 and 2 there is shown an illustrative embodiment of a zig-zag panel antenna system in accordance with the present invention. The antenna 3,375,525 Patented Mar. 26, 1968 comprises a pair of zig-zag radiative conductors 1 and 2 lying in a common plane and extending in opposite directions from a common feed or energization region 3 and a planar reflective conductor 4 spaced therefrom and in parallel relationship to the plane of the conductors 1 and 2. A coaxial transmission line 5 having an outer conduc tor 6 connected to a region of the reflector spaced approximately one-quarter of a wavelength from the region of the reflector adjacent the energization region 3 of the conductors 1 and 2, and an inner conductor 7 extending outward beyond the reflector and perpendicular thereto. A coupling plate or strap 8, to be described in greater de tail detail in connection with FIGURES 3 and 4, has one end connected to the radiative conductors 1 and 2 at the energization region 3 and the other end connected to inner conductor 7 of transmission line 5.

The radiative conductor 1 consists of twelve elements consecutively ordered or numbered 11 through 22, respectively, from the coupling plate 8 and each one-half wavelength long at the frequency of operation of the antenna. Similarly, the conductor 2 consists of twelve elements consecutively ordered or numbered 31 through 42, respectively, from the coupling plate 8 and each one-half wavelength long at the frequency of operation of the antenna. The acute angle between adjacent elements of each of the conductors may range from 60 to degrees. The conductors are supported in spaced relation to the refiector by a plurality of insulators 9 suitably spaced along the length of the conductors.

The spacing of the radiative conductors 1 and 2 from the reflector 4 is set so as to provide the desired radiation from the radiative conductors and is the primary consideration in setting the spacing of the radiative conductors from the reflective conductor. Generally such spacing is of the order of one-eighth of a wavelength at the frequency of operation thereof and may be greater or less. Of course, the greater the spacing the greater is the percentage of applied energy radiated from each element thereof, and conversely, the smaller the spacing the less is such percentage. Also the greater the spacing of the elements from the reflector the greater would be the input impedance thereof thus making it more difficult to match the impedance of such antenna to commonly available transmission lines. Even though the impedances of the radiative conductors are paralleled, the resultant impedance may be of the order of twice the characteristic impedance of commonly available transmission lines, and in addition the reactive component of the antenna input impedance may be quite significant requiring that such impedance be matched for an eflicient flow of energy from the transmission line to the antenna. For example, the input impedance of such an antenna may have a resistive component of ohms and a capacitive reactive component of 200 ohms. Capacitive reactance exists in the vicinity of the bends inthe conductors 1 and 2 and as these bends are spaced approximately one-half wavelength apart they add up at the energization end of the conductors. While such capacitances may be matched along the conductor by lumped capacitances appropriately spaced on the elements, means still have to be provided for matching the lumped capacitance at the energization end of the conductors 1 and 2.

One way of providing a matching of the complex impedance of the antenna system to the characteristic impedance of commonly available transmission lines is to insert a section of transmission line of a characteristic impedance substantially the same as the value of the resistive component of antenna-impedance and of a length to balance the reactive component of antenna impedance. By providing a one-quarter wave section having the characteristic impedance which is the square root of the product of the impedance of the antenna resistive component match is achieved. Another way of providing a match is a to insert between the transmission line supplying energization and the antenna a section of transmission line of a particular length and particular characteristic impedance at the frequency of operation of the antenna. In both such direct feed-through systems the sections of transmission line of different characteristic impedance could be provided by simply altering the diameter of the inner conductor of a coaxial transmission line. If the precise value of the antenna impedance is known and the matching sections of the transmission line are precisely made a desired match results. However such provisions are somewhat complex and should there be minor changes in frequencies and minor variations in dimensions of the antenna, tuning .must be provided in the transmission line sections to achieve an optimum match.

In accordance with the present invention a coupling plate or tuning strap 8 is provided between the input ends of the radiative conductors 1 and 2 and the inner conductor 7 of the coaxial transmission line supplying excitation to form with the reflective conductor of the antenna a transmission line. The plate 8 is contoured and spaced, as shown in detail in FIGURES 3 and 4, to have a tapered characteristic impedance line. A section 23 of the plate adjacent the radiative conductors 1 and 2 is tapered in spacing with respect to the reflective conductor 4 and a section 24 adjacent the inner conductor of the transmission line is relatively constant in spacing with respect to the reflector. However, the width of section 24 of the plate is tapered in the direction of the radiative conductors. Such an arrangement provides a transmission line with capacitance progressively increasing from the excitation ends of the conductors to the transmission line thereby forming a transmission line in which the characteristic impedance progressively decreases from a high value. at the input terminals to a relatively low value at the output terminals of the transmission line 5. The taper is arranged so that the transmission line 5 sees the resistive component of antenna impedance substantially of value equal to desired characteristic impedance. The plate- 8 is made of suflicient width about the point of connection 25 to the inner conductor of the transmission line so that the reactive component of the antenna seen at the load end of the transmission line appears as an inductance. Such inductance is tuned out by the provision of s-uflicient capacitance about the point of connection 25 as mentioned. Thus a match of the complex impedance of the antenna to the characteristic impedance of the transmission line is achieved.

It will be appreciated, if desired, other configurations could havelbeen used. The tapered transmission line i could 'have taken the form of a strap of relatively constant width and spacing with respect to the reflector progressively decreased to the inner conductor of the transmission line. Suflicient capacitance would, of course, be provided at the output terminal of the transmission line to match the reactive component of antenna impedance. In another alternative, the tapered transmission line could have taken the form of a strap in which the taper in characteristic impedance is provided solely by taper in the width of the strap. It will be appreciated that the lengths of strap as measured from the input terminals of the antenna to the conductor could be appreciably greater or smaller than one-quarter of a wavelength. For example, if the reactive component of antenna impedance were inductive then it would be desirable to use a tapered line length less than one-half wavelength but longer than one-quarter wavelength in order to permit matching of the inductive component with a lumped capacitance situated at the load end of the transmission line.

The conductive plate or strap 8 is bolted to the radiative conductors 1 and 2 by means of a pair of bolt assemblies 27 and 28. The end of the coupling plate adjacent the inner conductor 7 of the transmission line 5 has a of the conductors -1 and 2 into two halves as indicated 7 4' hole into which the threaded extension 26 of the inner conductor 7 of the transmission line fits. On this extension there is provided nut 29 which secures insulator 30 in place to provide support for the inner conductor 7 to seal off the transmission line from weather influences.

A pair of nuts 43 and 44, one on each side of the plate 8 permit adjustment of the section of the plate about hole 25 adjacent the inner conductor 7 in relation (to the conductive reflector 4 to provide an optimum match in the impedance of the antenna to, the transmission line.

If desired a slot may be located in the coupling plate extending along the length thereof for a partial distance and separating the parts thereof adjacent the input ends by the dotted line 45 to provide a path for current flow therethrough for the purpose of heating the plate and the conductors to prevent the formation of ice thereon. Also, if desired, the coupling elements could be completely enclosed in a conductive box to shield it from the weather and as well to eliminate radiation therefrom. In such an arrangement coupling probes maybe provided in the box for the purpose of tuning the strap to achieve the desired match in the impedance of the antenna to the impedance of the transmission line.

It will be appreciated that coupling strap could be used with helical antennas such as described in US. Patent 2,985,878. In such an antenna the radiative'conductors are spiral and the reflector is a cylinder. Accordingly the strap would have a cylindrical configuration insteadtof the generally planar configuration to provide the necessary taper in the characteristic impedance.

While the invention has been described in specific embodiments, it will be appreciated that many modifications may be made by those skilled in the art and we intend by the appended claims to cover allsuch modifications and changes as fall within-the true spirit and scope of the invention.

What we claim as new and desired to secure by Letters Patent of the United States is:

1. An antenna system comprising:

a pair of conductors each extending in opposite directions from a common region,

a reflector spaced in radiative relation with said pair of conductors to provide an antenna having a predetermined input impedance,

a transmission line forproviding energization to said antenna having a characteristic impedance lower in value than the input impedance of said antenna,

means for connecting one terminal of said transmission line to said reflector, means for connecting the other terminal of said transmission line to adjacent ends of said radiative conductors in said common region,

said means including a conductor being so formed and in spaced relation to said reflector to form a transmission line tapered inimpedance from said input impedance to said characteristic impedance.

2. An antenna system comprising:

a pair of conductors each extending in opposite direc tions from a common region,

a reflector spaced in radiative relation with said pair of conductors to provide an antenna having a predetermined input impedance,

a transmission line for providing energization to said antenna having a characteristic impedance lower. in value than the input impedance of said antenna,

means for connecting one terminal of said transmission line to said reflector,

ductor in said common region,

said means including a planar conductor in spaced relation to said reflector substantially one-quarter wavelength long at the frequency of operation-of said system and including a section adjacent said transmission line tapered in width in the direction of said common region and another section adjacent said common region tapered in spacing with respect to said reflector in the direction of said transmission line.

3. An antenna system comprising:

a pair of conductors each extending in opposite directions from a common region,

a reflector spaced in radiative relation with said pair of conductors to provide an antenna having a predetermined input impedance,

a transmision line for providing energization to said antenna having a characteristic impedance lower in value than the input impedance of said antenna,

means for connecting one terminal of said transmission line to said reflector,

means for connecting the other terminal of said transmission line to adjacent ends of said radiative conductor in said common region,

said means including a planar conductor in spaced relation to said reflector substantially one-quarter Wavelength long at the frequency of operation of said system and including a section tapered in width from said transmission line to said common region.

4. An antenna system comprising:

a pair of conductors each extending in opposite directions from a common region,

a reflector spaced in radiative relation with said pair of conductors to provide an antenna having a predetermined input impedance,

a transmission line for providing energization to said antenna having a characteristic impedance lower in value than the input impedance of said antenna,

means for connecting one terminal of said transmission line to said reflector,

means for connecting the other terminal of said transmission line to adjacent ends of said radiative conductor in said common region,

said means including a planar conductor in spaced relation to said reflector substantially one-quarter wavelength long at the frequency of operation of said system and including a section tapered in spacing from said reflector from said common region to said transmission line.

5. An antenna comprising:

a pair of conductors each extending in opposite directions from a common region,

a reflector spaced in radiative relation with said pair of conductors to provide an antenna having a predetermined input impedance including a resistive and reactive component,

a transmisison line for providing energization to said antenna having a characteristic impedance lower in value than the resistive component of input impedance of said antenna,

means for connecting one terminal of said transmission line to said reflector,

means for connecting the other terminal of said transmission line to adjacent ends of said radiative conductor in said common region,

said means including a planar conductor being so formed and in spaced relation to said reflector to form a transmission line tapered in impedance from said resistive component to said characteristic impedance, reactive means in the vicinity of said transmission line for tuning out said reactive component.

6. An antenna system comprising:

a pair of conductors each extending in opposite directions from a common region,

a reflector spaced in radiative relation with said pair of conductors to provide an antenna having a predetermined input impedance including a resistive and capacitive component,

a transmission line for providing energization to said antenna having a characteristic impedance lower in value than the resistive component of input impedance of said antenna,

means for connecting one terminal of said transmission line to said reflector, means for connecting the other terminal of said transmisison line to adjacent ends of said radiative conductor in said common region,

said means including a planar conductor substantially one-quarter wavelength long at the frequency of operation of said system being so formed and in spaced relation to said reflector to form a transmission line tapered in impedance from said resistive component to said characteristic impedance, a capacitance in the vicinity of said transmission line for balancing out said capacitive component.

7. An antenna system comprising:

a pair of conductors each extendingin opposite directions from a common region,

a reflector spaced in radiative relation with said pair of conductors to provide an antenna having a predetermined input impedance including a resistive and capacitive component,

a transmission line for providing energization to said antenna having a characteristic impedance lower in value than the resistive component of input impedance of said antenna,

means for connecting one terminal of said transmission line to said reflector, means for connecting the other terminal of said transmission line to adjacent ends of said radiative conductor in said common region,

said means including a planar conductor substantially one-quarter wavelength long at the frequency of operation of said system being so formed and in spaced relation to said reflector to form a transmission line tapered in impedance from said resistive component to said characteristic impedance, a lumped capacitance in the vicinity of said transmission line for balancing out said capacitive component.

8. An antenna comprising:

a pair of conductors each extending in opposite directions from a common region lying in a common plane, each conductor including a plurality of gen erally linear elements approximately one-half wavelength long at the frequency of operation of the antenna,

the elements of each of said conductors being serially connected,

even ordered elements of one of said conductors and odd ordered elements of the other of said conductors with reference to said region being oriented in one general direction,

odd ordered elements of said one conductor and said even numbered elements of said other conductor being oriented in another general direction,

a planar reflector spaced in radiative relationship with said pair of conductors to provide an antenna having a predetermined input impedance,

a transmission line having a pair of terminals for providing energization to said antenna having a characteristic impedance lower in value than the input impedance of said antenna,

means for connecting one terminal of said transmission line to said reflector,

means for connecting the other terminal of said transmission line to adjacent ends of said radiative conductor,

said means including a planar conductor being so formed and in spaced relation to said reflector to form a transmission line tapered in impedance from said resistive component to said characteristic impedance, reactive means in the vicinity of said transmission line for tuning out said reactive component.

9. An antenna comprising:

a pair of conductors each extending in opposite directions from a common region lying in a common plane,

each conductor including a plurality of generally linear elements approximately one-half Wavelength long at the frequency of operation of the antenna,

the elements of each of said conductors being serially connected,

even ordered elements of one of said conductors and odd ordered elements of the other of said conductors with reference to said region being oriented in one general direction,

odd ordered elements of said one conductor and said even numbered elements of said other conductor being oriented in another general direction,

a planar reflector spaced in radiative relationship with said pair of conductors to provide an antenna having a predetermined input impedance,

a transmission line having a pair of terminals for providing energization to said antenna having a characteristic impedance lower in value than the input impedance of said antenna,

means for connecting one terminal of said transmission line to said reflector,

means for connecting the other terminal of said transmission line to adjacent ends of said radiative conductor,

said means including a planar conductor substantially one-quarter wavelength long at the frequency of operation of said system being so formed and in spaced relation to said reflector to form a transmission line tapered in impedance from said resistive component to said characteristic impedance, capacitive means in the vicinity of said transmision line for balancing out said reactive component.

References Cited UNITED STATES PATENTS 20 ELI LIEBERMAN, Primary Examiner. 

1. AN ANTENNA SYSTEM COMPRISING: A PAIR O CONDUCTORS EACH EXTENDING IN OPPOSITE DIRECTIONS FROM A COMMON REGION, A REFLECTOR SPACED IN RADIATIVE RELATION WITH SAID PAIR OF CONDUCTORS TO PROVIDE AN ANTENNA HAVING A PREDETERMINED INPUT IMPEDANCE, A TRANSMISSION LINE FOR PROVIDING ENERGIZATION TO SAID ANTENNA HAVING A CHARACTERISTIC IMPEDANCE LOWER IN VALUE THAN THE IMPUT IMPEDANCE OF SAID ANTENNA, MEANS FOR CONNECTING ONE TERMINAL OF SAID TRANSMISSION LINE TO SAID REFLECTOR, MEANS FOR CONNECTING THE OTHER TERMINAL OF SAID TRANSMISSION LINE TO ADJACENT ENDS OF SAID RADIATIVE CONDUCTORS IN SAID COMMON REGION, SAID MEANS INCLUDING A CONDUCTOR BEARING SO FORMED AND IN SPACED RELATION TO SAID REFLECTOR TO FORM A TRANSMISSION LINE TAPERED IN IMPEDANCE FROM SAID INPUT IMPEDANCE TO SAID CHARACTERISTIC IMPEDANCE. 